Processed crystals have increased in demand due to their usefulness as a substrate in a variety of electronic components such as gallium nitride-compound semiconductors. Such uses, however, require the crystal substrate surface to be precisely oriented. In order to achieve a precise orientation, the crystal substrate must be meticulously processed. X-ray goniometers have been indispensable in this regard, as instruments used to determine the correct crystal plane prior to processing.
An x-ray goniometer is an apparatus designed to measure the angle between crystalline orientation. It comprises an x-ray source, a collimator, a specimen, and an x-ray detector. The collimator confines the x-ray source to a narrow beam that is directed toward the specimen. As the x-rays encounter the specimen, some are diffracted toward the detector. The diffracted x-rays behave according to the Bragg Equation:nλ=2d(sin θ)where lambda, λ, is the wavelength in Angstroms of the diffracted x-rays, theta, θ, is one-half of the diffraction angle 2θ, and is the angle between the incident x-rays and the scattering planes. The distance between the crystalline lattice planes, d, is measured in Angstroms.
There are many difficulties associated with the manufacture and processing of monocrystalline materials for use in electronic devices. For example, the process begins when a crystal boule is placed on a platform and an x-ray goniometer is used to measure the orientation of the crystals. After the crystal orientation has been determined, the boule is marked and adhesive is used to rigidly and removably secure the boule to a machine fixture, in order to maintain proper orientation of the boule with respect to the drilling machine. The machine fixture commonly consists of an aluminum or graphite board. After the boule is fixed to the machine fixture and loaded into the core drilling machine, the crystal orientation is again measured to ensure that the boule has not shifted its position during the curing process for the adhesive. If the boule does not remain oriented correctly, as is often the case, it must be forcibly removed from the substrate and the process is repeated, wasting precious time and resources. This process continues until the boule is aligned and fixed properly to the substrate. Often this can take 7 to 10 repetitions or more until the boule is positioned correctly.
Once positioned correctly, the boule is then transferred to a core drilling machine, which produces cylindrically shaped ingots. The final orientation for the ingot must be accurate, within a tolerance of ±2 arc-minutes, or 1/30 of a degree. To correct for variability of crystal orientation, conventional processing will commonly produce an ingot that is substantially larger than needed. The ingots will again be measured with an x-ray goniometer and their surfaces will be ground further to produce an ingot with the required orientation. This often requires numerous measurement-grinding iterations.
What is lacking in the prior art is a system and machine assembly which does not make use of this repetitive and iterative process of drilling, grinding, or other crystal machining and still maintains proper crystal orientation throughout processing. This is accomplished by integrating the functions of crystal structure determination and automatic alignment of the crystal into the processing machine. A number of patents and disclosures relate or refer to this area and crystal processing.
The McCarty Patent, U.S. Pat. No. 2,425,750, discloses a device for aligning a crystal using light, wherein a cutting tool can replace the aligning tool after the crystal is measured. This reference does not disclose a tool using x-rays, or a tool that has both the cutting tool and the measuring tool integral to the assembly.
The Coleman Patent, U.S. Pat. No. 2,556,167, discloses a crystal analysis apparatus that has an improved jig for holding crystals while determining their orientation and facilitates easy transfer to a cutting surface. It does not disclose a device where an x-ray goniometer and cutting tool are combined into one tool.
The Kumada Patent, U.S. Pat. No. 3,838,678, discloses an apparatus where a crystal is measured with x-ray radiation and then moved onto a separate area with a cutting device at a predetermined angle. This reference does not disclose an apparatus having an x-ray goniometer which is able to measure a crystal without having to subsequently move the crystal to process it.
The Frederick Patent, U.S. Pat. No. 4,002,410, discloses a small device to removably secure a crystal in order to determine the orientation for sawing by transmitting a series of light beams and interpreting the pattern. It does not disclose a device that has an integrated measurement and sawing tool, nor does the disclosed device utilize x-rays to determine crystal orientation.
The Causey Patent, U.S. Pat. No. 4,331,452, discloses a crystal shaping apparatus having means for x-ray determination of crystal orientation and an apparatus to grind an orientation flat upon the wafer, thereby creating a crystal blank. This reference does not disclose a device with a built in x-ray crystal detection device for cutting or grinding a crystal.
The Brinkgreve Patent, U.S. Pat. No. 4,637,041, discloses an x-ray analysis apparatus with a rotatable arm for which the mutual displacement and orientation of components is executed in such a manner that it permits reproducible adjustment of the components with respect to one another. It does not disclose an x-ray analysis tool with integrated crystal processing tools.
The Rinik Patent, U.S. Pat No. 4,649,556, discloses a method and apparatus for “on-line” nondestructive measurement of grain size of various materials using a monochromatic beam of x-rays to allow actions such as corrective actions to quickly occur, and measure moving materials. It does not disclose a goniometric method of determining crystallographic orientation, or a crystal processing apparatus.
The Howe Patent, U.S. Pat. No. 4,788,702, discloses a method for determining the orientation of a single crystal which utilizes a crystal on a turntable and a stationary position-sensitive detector which is able to complete this process in a completely automated manner. This reference does not disclose a measuring device that is integrated into a processing device.
The Vanderwater Patent, U.S. Pat. No. 4,884,887, discloses a method of determining crystal orientation which uses the processing machine as a reference frame to simplify the process, and further uses a U-shaped member, which when held at a particular distance, causes the body of the crystal to come into contact with both ends of the member. It does not disclose a method which incorporates both crystal orientation determination and crystal processing in one apparatus.
The Ibe et al. Patent, U.S. Pat. No. 5,187,729, discloses a method and apparatus for determining the orientation flat of a crystal by rotating the ingot about a single axis only, using x-ray diffraction to determine the orientation, and then grinding the orientation flat. It does not disclose a method whereby x-ray analysis is integrated into subsequent polishing or cutting steps; nor does it disclose a method for crystal processing of boules or wafers.
The Hirano Patent, U.S. Pat. No. 5,405,285, discloses a machine error correction apparatus in which machine errors are measured and then transmitted into the memory of a grinding device, which uses that information to correct the errors while grinding. This invention does not disclose a grinding device combined with an orientation measurement device.
The Hirano Patent, U.S. Pat. No. 5,484,326, discloses a method for processing a crystal whereby a crystal is ground down, measured with x-rays to determine its orientation, and then subsequently ground with an orientation flat. This reference does not disclose a method where a crystal cutting or polishing process includes an integrated x-ray analysis apparatus.
The Miller Patent, U.S. Pat. No. 5,529,051, discloses a method of preparing wafers where silicon wafers are sawn from ingots on the (100) reference plane, using the reference planes to determine ingot orientation, as opposed to x-ray analysis. This reference does not disclose a method of producing crystal wafers using x-ray analysis in conjunction with a method of processing ingots.
The Grueninger Patent, U.S. Pat. No. 5,640,437, discloses a goniometer with a radiation detector, a Bragg Detector, and a fluorescent detector combined into one device. This device does not include any additional functions for cutting or otherwise processing boules, ingots, or wafers.
The Hauser Patent, U.S. Pat. No. 5,720,271, discloses a process and apparatus for orienting a crystal to a particular cutting plane by orienting it on cylinders and positioning it over a plate and then cutting it in accordance with that orientation. This device does not disclose an x-ray analysis tool with integrated crystal processing tools.
The Shahid Patent, U.S. Pat. No. 5,768,335, discloses an apparatus and method for measuring the degree of misorientation of the polished surface of a single wafer by utilizing both an optical beam and an x-ray beam to ascertain the difference between the reflected and diffracted beams with a measuring device containing a detector aligned along a track. This apparatus and method does not disclose any processing steps such as cutting or grinding being carried out by the same device that measures a crystal.
The Hauser Patent, U.S. Pat. No. 5,839,424 discloses, the use of a process and device for positioning several single crystals on a support for simultaneous cutting utilizing a machine having a rotatable frame, a gripping device carrying single crystals, a rotatable gripping support and a cutting tool. However, this disclosure does not mention or teach the use of an x-ray goniometer in conjunction with the crystal positioning and cutting device. The positioning device in the invention is outside the cutting machine.
The Katamachi et al. Patent, U.S. Pat. No. 5,893,308, discloses the use of a bonding jig which is used to bond a crystal ingot thereto prior to cutting the piece. The horizontal and vertical surfaces of the work piece bonding block may be aligned parallel to each other. The block is then fed through a wire saw. The bonding jig may be tilted to adjust the work piece so that the central axis is inclined against the cutting plane at a predetermined angle on the basis of shift value data of the crystal orientation. This disclosure does not teach orientation measurement and determination within a crystal processing machine.
The Nagatsuka et al. Patent, U.S. Pat. No. 5,904,136, discloses the use of a method and apparatus for cutting crystals which comprises a workpiece which is attached to a workpiece feed table which is fed through a wire saw, wherein the tilt angle of the workpiece has been adjusted based upon the predetermined crystal orientation outside the wire saw area. The wire saw utilizes a plurality of grooved rollers to form a wire row. The workpiece is attached to a feed table which may reciprocate with respect to the wire row. In this disclosure, however, the crystal orientation has been determined outside the crystal machining area.
The Muramatsu Patent, U.S. Pat. No. 5,927,263, discloses the use of a method for manufacturing circular wafers wherein a specified crystal orientation is detected and the crystal is then mounted upon a support table in accordance with the detected crystal orientation. Subsequently, a recognition mark is made upon the top face of the crystal in accordance with a position of the support. Finally, the support is cut and the workpiece removed. In this disclosure, however, the crystal orientation has been determined outside of the crystal processing area.
The Banzawa Patent, U.S. Pat. No. 6,024,814, discloses a method where an ingot is analyzed with a goniometer, and then removably secured to an intermediate base according to the results of that analysis, thereby properly aligning it with a saw. This patent does not disclose an apparatus or method for measuring an ingot and subsequently processing it without moving the sample in iterative intervening steps.
The Banzawa Patent, U.S. Pat. No. 6,056,031, discloses a method where an ingot is measured with an x-ray goniometer, and then transferred to an intermediate surface in a matter which preserves the information about the orientation of the crystal for later processing. It does not disclose a method of measuring and processing an ingot without an intermediate transfer from one supporting plate to another.
The Katamachi Patent, U.S. Pat. No. 6,145,422, discloses a work piece on a block which is then processed by a wire saw, and it further discloses prior art where gonio angle measuring meters are mounted on the respective wire saws. This reference does not disclose an x-ray goniometer used with grinding or other processing steps. Nor does this reference provide for continuous feedback of gonio angles.
The Olkrug Patent, U.S. Pat. No. 6,159,284, discloses a process and device for producing a semiconductor wafer by rotating a cylindrical crystal ingot along two planes of rotation, then the single crystal is secured by pads on either end of the crystal and ground to a uniform diameter. This reference does not disclose the use of an x-ray goniometer directly in association with a grinding machine.
The Banzawa Patent, U.S. Pat. No. 6,182,729, discloses the use of an apparatus for manufacturing a plurality of wafers by slicing a cylindrical ingot with a wire saw. The device consists of a measuring device for measuring crystal orientation of the ingot, and an adhering device to removably secure the ingot to an intermediate plate and a support place. This invention does not disclose the use of an orientation measuring device integrated with a crystal processing machine.
The Blank et al. Patent, U.S. Pat. No. 6,888,920, discloses the use of a low cost high precision goniometric device for use in x-ray diffractography or optical systems which comprises a spherical sector supported on at least one bearing, a top surface for mounting an object thereto, a center of rotation within an object, a rod or other member disposed below the spherical bearing surface, motors or actuators to animate the device and a linkage between the rod and the motors. This particular disclosure does not mention or teach any method suitable for determining crystal orientation during cutting, grinding or polishing processes.
The Beanland et al. Patent, U.S. Pat. No. 6,977,986, discloses the use of a lithographic tool for printing a pattern from a mask onto a wafer together with an x-ray diffraction tool for determining crystal orientation. Because the apparatus does not utilize any flats on the wafer for angular alignment purposes, it achieves a higher degree of accuracy when aligning crystal planes. Again, this particular disclosure does not teach the use of an x-ray crystal alignment device which is integral to the machine performing cutting, polishing or grinding operations upon a crystal substance.
The Beanland Patent, U.S. Pat. No. 7,072,441, discloses the use of a method of alignment for aligning crystalline substances to form lithographic features thereupon including the steps of measuring the orientation of a flat; measuring a crystallographic plane orientation of the substrate, determining an error angle; registering the flat via a lithographic tool, rotating the crystalline substance by the error angle and marking one or more features on the substance using the lithographic tool, thereby angularly aligning the feature layers to the plane orientation. However, this disclosure does not mention or teach any means for using an x-ray crystal alignment device which is integral to the machine performing a cutting, polishing or grinding operation thereupon.
The Hammer et al. Patent, U.S. Pat. No. 7,137,865, discloses the use of a method for the division of single crystals where a crystal that is to be cut into at least two parts and a cutting tool are moved relative to one another wherein the crystal will lie in the cutting plane which is characterized by an angle □ between the crystal's direction and the direction of advancement that is chosen to minimize cutting tool forces on the crystal to be cut. However, this disclosure does not teach the determination of crystal orientation in the machine utilized for processing the crystal, but rather the crystal is mounted and its orientation is determined prior to the processing step.
The Kikuchi et al. Patent, U.S. Pat. No. 7,158,609, discloses the use of an x-ray crystal orientation measuring apparatus for mounting the crystal upon a stage or platform for later processing. Again, the processing machine for the crystal does not have an orientation device which is integral to the machine.
Finally, the Bradazcek et al. Patent, U.S. Pat. No. 7,285,168, discloses the use of a method and apparatus for the determination of crystal orientation of very hard materials such as sapphire or silicon carbide. A crystal specimen is placed upon a revolving table for determining the crystal lattice orientation by rotating the table through at least one complete revolution. Subsequently a second crystal (or more) may be stacked atop the prior crystal so that multiple crystal items may be further processed at the same time. However, this particular disclosure does not teach any means for incorporating a crystal orientating device within a cutting, polishing or grinding machine.
However, nowhere in the prior art is there seen a system or assembly wherein an x-ray goniometer has been effectively incorporated into a machine which is utilized for the processing of crystalline substances in order to assure high precision alignment of the interior crystalline orientation during processing. Further, nowhere in the prior art is shown an intelligent machine which continually processes information received from an x-ray goniometer, and adjusts the crystalline substance accordingly for the purpose of ensuring proper crystal alignment during the entire process of machining a crystalline substance.